The Trenergy project was chosen in the context of a call for proposals launched by the French national research agency as part of its “sustainable transport and mobility” programme. A multi-faceted partnership between Alstom, Enogia and DynFluid (the Arts et Métiers’ fluid dynamics laboratory), it started on March 19th, 2013, for a duration of three years.

Over half of the European rail network is not electrified, above all many regional lines. Trenergy aims at recovering the heat released by the exhaust fumes of diesel-electric train engines through an organic Rankine cycle, thus increasing their energy efficiency. It should allow Alstom to commercialize more energy-efficient diesel-electric-fuelled trains.

A step toward energy transition

This project aims at improving electric efficiency in trains. Not only are rail networks being improved to reduce friction, but research is also being conducted on how to recover part of a train’s kinetic energy, for instance whenever the brakes are used, yielding successful initial results. Since 2007, Alstom has thus been manufacturing trains which use 10% less electricity by converting part of the heat released by brakes into electricity. Other brake-related solutions “can yield savings of up to 30%”. ZEFIRO, the high-speed train manufactured by Alstom’s competitor Bombardier, is yet another example, “with efficiency gains up to 50%”.

The organic Rankine cycle, a technology at the heart of the Trenergy project

The working principle of the organic Rankine cycle is similar to that of a thermal power plant, where water is heated and turned into steam to drive a turbine and generate electricity; but instead of water, the organic Rankine cycle uses an organic (carbon-based) fluid, which offers a number of advantages: it allows for electricity generation at a lower temperature (80°C), its expansion is higher, i.e. it moves faster through the turbine, its high density yields higher performance, even for low powers, and it dries faster, thus generating no condensation and minimizing wear. “To date, Rankine systems are mainly used for stationary equipment (power plants, heat recovery in boilers, ovens…) or ships. Several scientific and technical hurdles must be overcome before they can be considered a profitable method of increasing energy efficiency”, according to project coordinator FP Energies Nouvelles, a public research agency specialized in innovation and training in the energy, transportation and environment sector. Meanwhile, the start-up company Enogia has developed a promising micro-turbine design.

Promising lines of research

The Trenergy project is organized into three main research orientations: